presence_new/Presence.Desktop/Views/GroupView.axaml

<UserControl xmlns="https://github.com/avaloniaui"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:vm="using:Presence.Desktop.ViewModels"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        mc:Ignorable="d" d:DesignWidth="800" d:DesignHeight="450"
        x:Class="Presence.Desktop.Views.GroupView"
        x:DataType="vm:GroupViewModel">

    <Design.DataContext>
        <vm:GroupViewModel/>
    </Design.DataContext>
	<DockPanel Background="Azure">
		<StackPanel DockPanel.Dock="Bottom">
			<TextBlock Text="List ↑" HorizontalAlignment="Center"/>
			<TextBlock Text="{Binding Users.Count, StringFormat='Количество студентов: {0}'}" 
			   HorizontalAlignment="Left" 
			   Margin="10,10,0,0"
			   Foreground="Black"
			   IsVisible="{Binding SelectedGroupItem, Converter={x:Static ObjectConverters.IsNotNull}}"/>
			<Button Content="Перейти к посещаемости" 
					Command="{Binding NavigateToPresenceCommand}"
					HorizontalAlignment="Right"
					Margin="0,10,0,0"
					Foreground="Black"/>
		</StackPanel>
		<StackPanel 
			Spacing="10"
			HorizontalAlignment="Center"
			DockPanel.Dock="Top"
			Orientation="Horizontal">
			<TextBlock Text="Combobox ->"/>
			<ComboBox  ItemsSource="{Binding Groups}" SelectedValue="{Binding SelectedGroupItem}">
				<ComboBox.ItemTemplate>
					<DataTemplate>
						<TextBlock Text="{Binding Name}"/>
					</DataTemplate>
				</ComboBox.ItemTemplate>
			</ComboBox>
			<Button  Width="100" Command="{Binding OpenFileDialog}"/>
			<ComboBox/>
		</StackPanel>
		<Border>
			<ListBox SelectionMode="Multiple" Selection="{Binding Selection}" Background="Bisque" ItemsSource="{Binding Users}"> 
				<ListBox.ContextMenu>
					<ContextMenu>
						<MenuItem 
							IsVisible="{Binding !MultipleSelected}" 
							Header="Remove" 
							Command="{Binding RemoveUserCommand}"
							CommandParameter="{Binding Selection.SelectedItem}"
							Foreground="Black"/>
						<MenuItem 
							IsVisible="{Binding !MultipleSelected}" 
							Header="Edit" 
							Command="{Binding EditUserCommand}"
							CommandParameter="{Binding Selection.SelectedItem}"
							Foreground="Black"/>
						<MenuItem 
							IsVisible="{Binding MultipleSelected}" 
							Header="RemoveAll" 
							Command="{Binding RemoveAllSelectedCommand}"
							Foreground="Black"/>
					</ContextMenu>
				</ListBox.ContextMenu>
				<ListBox.ItemTemplate>
					<DataTemplate>
						<StackPanel Orientation="Horizontal">
							<TextBlock Text="{Binding Name}" Foreground="Black"/>
						</StackPanel>
					</DataTemplate>
				</ListBox.ItemTemplate>
			</ListBox>
		</Border>
	</DockPanel>
</UserControl>